The American Cancer Association estimates that 1.5 million citizens of the US are diagnosed with cancer each year. Approximately 50% of these cancer patients will undergo radiation therapy, which can provide definitive local regional tumor control, thus affording these patients with a durable progression free survival. Unfortunately, many tumors do not respond to irradiation. Elucidating the molecular mechanisms responsible for radiation therapy's failure to control tumor growth requires a critical understanding of Radiation Biology, a multi- disciplinary science that studies physics, biology, and medicine as it pertains to oncogenesis, tumor biology and normal tissue physiology. As important as Radiation Biology is for supporting Radiation Oncology's mission, there are very few such training programs in this country. The goal of this training grant is to continue to teach Postdoctoral Fellows to perform independent research in the area of Radiation Biology, so that they can make outstanding contributions to the fields of Radiation Oncology and Cancer Biology. We propose to accomplish this using a multi-faceted approach consisting of 1) training in the laboratories of outstanding scientists who utilize cutting edge techniques coupled with highly collaborative approaches, 2) multi- disciplinary seminar series designed to foster interactions between basic scientists and clinician/scientists who perform translational research, 3) didactic training in the areas of Radiation Biology, Radiation Physics, and Cancer Biology, 4) a grant writing workshop, 5) professional development, 6) training in laboratory management, and 7) Training in the Responsible Conduct of Research. Trainees must have completed a MD and/or a PhD prior to entering the program. The program is designed to train 3 Fellows for a duration ranging from 2 to 3 years. It is anticipated that 2 of the trainees will have just completed their PhD or MD and the third trainee will have 2 or 3 years Post Doctoral experience prior to entering our program. To date 70% of trainees who complete training tenure track assistant professors, staff scientists at pharmaceutical companies, or Radiation Oncology Residents on track to attain faculty positions. Of note, 30% of the trainees who have accepted offers to this program have been underrepresented minorities. Based on these successes, we submit that this training grant program is fulfilling the goals of the National Ruth L. Kirschstein National Research Service Award.